Micro Electro Mechanical Systems (MEMS) processing is being investigated as an alternative for fabricating extreme ultraviolet (EUV) transition radiation laser (TRL) and transition radiation oscillator (TRO) structures. Using conventional MEMS deposition and etch processes, TRO (or TRL) structures can be fabricated by forming multilayered, spaced-apart membranes over a substrate. When the membranes are placed in the path of a mildly relativistic electron beam, a coherent superposition of transition radiation having a predetermined wavelength (for example, extreme ultraviolet (EUV) wavelengths around 13 nanometers), can be produced at the structure's output. Such structures can be used as EUV illumination sources in various applications, such as EUV lithography and EUV interferometry.
During operation of systems that use MEMS TRO and TRE structures, temperatures can exceed 1000 degrees Celsius. At these temperatures, membranes can deform relative to each other. Such deformation can destroy the periodicity of the multilayered membrane stack and impact the performance of the system that houses the structure.
Shown in FIG. 1 is a prior art TRO (or TRE) structure 100 having membranes 120 and 121 exhibiting deformation due to thermal stress. As shown in FIG. 1, edges 101 of membranes 102 are adjacent posts 104, and each membrane 102 is separated by a vacuum region 103. Posts 104 overlie an etch stop layer 106. And, etch stop layer 106 is formed over substrate 108. Substrate 108 has an electron beam port opening 110 through which an electron beam 112 is projected. When the electron beam crosses the interface between two mediums (i.e. the interface between the vacuum region 103 and membrane 102), forward directed radiation (e.g., transition radiation) is created and is emitted from output region 119.
Under normal operating conditions, the heat generated in TRO and TRE structures can cause membranes to deform (i.e. bend 120 or buckle 121). These membranes shape changes can impact the structure's performance by producing aberrational output radiation 116, which differs from the sought after output radiation 114. The effects of this aberrational output radiation 116 can include a shift in peak output intensity of the electron beam, degradation of the transmission of coherent light, or a shift in output wavelength.